I'd personally at least give them a chance. Defederating is a pretty easy process and can be performed at any point in time. At least some Threads users may as well get to know about Lemmy and switch to it.
Upd: yes I do understand many people don't trust Meta and neither do I. But I also understand lots and lots of users here are using anonymous accounts, and federation information is already public to begin with. Combining the fact that Fediverse may gain more than it may lose, including more users, original content, recognition and etc, I generally think it's worth the risk. I am generally content with any decision, just sharing my two pennies of thought.